Radio aerial system



Fig.4

0 BGHM RADIO AERIAL SYSTEM Flled July 11 1939 July 1, 1 941.

Patented July 1, 1941 U ITED STATES, PATENT m;

' Otto Biihm, Hillwood Grove, Hutton, Brcntwood, England, assignor to: Radio Corporation of America, a corporation of Delaware I v Application July 11, 1939, Serial No. 283,780

In Great Britain August 8, 1938 5 Claims. ,(01. 250-11) This invention relates to radio aerial systems and has for its'obiect to provide improved and comparatively simple radio aerial systems of high efiiciency forthe space occupied and adapted to give a good concentration of radio energy in a desired predetermined direction.

There are broadly speaking two types of radio aerial systems adapted 'to' concentrate the radiated-energy in a desired predetermined: direction, the said two types being: 1') that in which the component 'radiators'of-the system are energized by standing waves, and (2):;that in which the component radiators of the system are energized by travelling or progressive waves. The former type of system, of which the well known parallel dipole beam aerial system is a typical example, is highly efiicient in that the concentration of energy radiated from the component radiators'to produce the concentrated beam in the required direction takes place in space and is therefore without noticeable loss, but on the other hand the said type of system is highly dependent on frequency, structurally complex, and expensive. The second type of system which is typified by the well known rhombic aerial terminated by a resistance equal to its own surge impedance, is in general simpler-and structurally more convenient and inexpensivethan the standing wave type of aerial, buton the other hand the sharp polar diagram obtained is accompanied by losses in the terminating resistance and accordingly the efliciency is not so good. v

According to thisinvention a radio aerial system comprises a plurality of component aerials each of the progressive wave type and energized with currents of such phasethatfthe currents at corresponding points in the individual component aerials are in phase with the radiation in the transmitting direction. The component aerials are preferably of the rhombic. type and may be placed end to end along the direction of transmission and fed in series, the arrangement being such that the currents .at corresponding points of the rhomb-uses are in phase with theradiation in the transmitting direction, the last rhombus only being terminated by an ohmic resistance equal to the surge impedance of the conductors leading thereto; or alternatively the rhombic or other travelling wave aerials may be located along a line perpendicular to the direction of transmission and fed in parallel and in equal phase, the rhombuses overlapping and each being terminated by a resistance equal to the surge impedance of the conductors. Preferably in the series arrangement-with the rhombic or other aerials in the desired line of transmission; the said' aerials also overlap.

The preferred embodiments of the invention employ, as already stated, rhomb-icaerials and for simplicity in description it will be assumed in what follows that rhombic aerials are used, though it is to be. understood that the invention maybe carried into effect with other similar types of progressive or travelling wa'ye aerials-T- The following description will aid in an understanding of the basic principles of the invention. The field strength E in the axial direction of a rhombic aerial is given by the following :expres 24O /D +B +D [1r 3 Q E=- I--- S111 s r B. a 2 /DH-BH-D Wherein Sis the distance from the transmitter; I'the cur'ren't strength; D thelength of the rl'iombus; B the breadth of the rhombus and-X the wavelength. 'Iithe dimensions are chosen in the usual way so that the expression in square'brackets for the desired wavelength to is equal to /2, the field strength E is proportional to'the breadth of the rhombus and is given by;

The input power Pr is given by:

PT'=ZoI where Z0 is the surge impedance which, fora normal-Vrhombus, is about 800' ohms. r

It is important to note that the input power' is independent of the dimensions of the rhombus and accordingly of the radiated power. 7

From the conditions above set out, it will be seen that the length and breadth of the rhombus 'are determinedbythe expression. r

Hence, for a given 'per'centagein crease 'i'nlength there isra smaller percentage increase in breadth, and'therefore field strength, which is proportional thereto. 3

The invention is illustrated in and further exa plai-ned in connection"with the accompanying drawing, in which-Figure 1 illustrates an'embodi ment of the present invention; Figures 2 and .3 illustrate modifications of Figure 1 wherein the aerials are overlapped laterally; Figure 4 illustrates a: longitudinally overlapping array; while Figure 5 illustrates a modification which is a combination of Figures 2 and 4 and Figure 6 is a further modification of Figure 4.

Suppose that in place of using a large rhombic aerial of length D and of breadth B there are employed, in accordance with this invention, a plurality-say three-small rhombic aerials of overall length D and arranged as shown in Figure 1 in the direction of transmission, the feeders being connected at the beginning of one rhombic aerial, the beginning of each aerial (except the first) being connected to the end of the preceding aerial and the last rhombic aerial being terminated by a suitable resistance R of resistance equal to the surge impedance of the conductors leading thereto so that all the rhombic aerials are in series, all the said rhombic aerials having equal currents of such phase that the currents at corresponding points of the individual rhombuses are in phase with the radiation in the transmitting direction. Then, with this multi-rhombus arrangement the field strength in the desired direction will be considerably greater than that of the single large rhombus replaced (this is represented in Figure 1 in broken lines at X) while, moreover, the breadth B of the aerial system, being the same as that of one small rhombus, will be substantially less than the breadth B of the large rhombus replaced.

Owing to the damping due to radiation, the current in the rhombuses decreases as the last rhombus is approached and the gain therefore is not quite as great as would appear if the currents were assumed equal. This attenuation of current in successive rhombuses introduces a practical limit to the number of rhombus elements which can with advantage be provided.

Suppose, for example, the space at disposal has a length D equal to six times the wavelength. Then the breadth of a single rhombus of length D will be 3.6 times the wavelength. By replacing this rhombus by two series loonnected rhombuses arranged as above described and each of length equal to three times the wavelength, the breadth will be reduced to 2.6 times the working wavelength. If the average current strength in the second rhombus is only 80 percent of that in the first, the ratio of the field strengths of the two rhombuses to that of the single rhombus replaced will be 1.3. Thus by replacing the single large rhombus by two small ones as described, an increase in field strength of substantially 30 percent is obtained. To produce the same increase in output power with the single rhombus it would be necessary to increase the input power by substantially 69 percent.

Substantial advantage can be obtained by using rhombuses side by side and overlapping. It might at first sight be thought-from a comparison with dipole aerials that overlapping is not a practical expedient, for if two dipoles are brought close together so as to overlap, the input increases owing to their mutual influence. This, however, is not the case with traveling wave aerials. If two rhombuses are brought close together so as to overlap, the input power is not affected by the increase in radiation resistance due to their mutual influence and there fore rhombuses overlapping present the same efficiency as when widely separated, provided, of course, that the distance between the two rhombuses is not made so small that corresponding wires in the two said rhombuses begin to be regardable as a single wire. Accordingly in another and preferred embodiment of the invention illustrated in Figure 2 two, or more than two, series rhombus arrangements as already described are arranged side by side so as to overlap each series arrangement being fed with feeders at its beginning and each being terminated with a suitable resistance R at the far end. If, as in the previous quantitatively discussed case the length D of a large single rhombus to be replaced is six times the working wavelength and the breadth B thereof is 3.6 times the working wave length, then by replacing this single rhombus by four rhombuses two in series and two in parallel, one series arrangement being by the side of and overlapping the other, the ratio of the field strength of the four rhombuses to that of the single rhombus replaced thereby will be 1.84.

In yet another embodiment of the invention shown in Figure 3 a plurality of rhombus aerials, each terminated by a suitable resistance are arranged overlapping and side by sidei. e. along a line perpendicular ;to the desired direction of transmission-being fed in parallel.

As regards the embodiment of Figure 3 if B is the breadth of the available space and this space were occupied by a single large rhombus X, the efiiciency would be measured by B /P Where P is the input power. Suppose, however, that the single rhombus is replaced by 12 small overlapping rhombuses side by side, and fed in parallel, each rhombus having breadth B. The total input power is now nP and the equivalent breadth nB'. Therefore, the efliciency is given L mm nP P Obviously, so long as B is greater than there will be a gain in efiiciency as compared to the known single large rhombus X.

It will now be seen that among the embodiments of the invention are: (a) a plurality of rhombuses in series, lying along the direction of transmission, the last being terminated by a suitable resistance; (b) a plurality of rhombuses in series lying along the direction of transmission and overlapping, the last being terminated by a resistance R (such an arrangement is shown in Figure 4); (c) a plurality of rhombuses side by side and overlapping, each being terminated by a resistance R (see Figure3) and, (d) combinations of (a) and (c) or (b) and (0) (such a combination is illustrated in Figure 2). Figure 5 shows, with actual dimensions a satisfactory aerial system designed to give an optimum wavelength of 17.85 meters for service on 15 meters and 22 meters (at either service wave length the field strength is at 10% less than with the optimum wavelength for the same input). The height of the aerials above ground is 61. There are four rhombus aerials (shown in full lines). Still further improvement could be obtainedat the cost, however, of increased utilization of spaceby providing two more as shown in broken lines. Figure 6 shows a further possible embodiment of the invention.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

l. A radio aerial system comprising a plurality of traveling wave antennas located along a line perpendicular to a desired direction of transmission and fed in parallel and in equal phase, the said antennas overlapping along said line and each being terminated by a resistance having a value equal to the surge impedance of the antenna connected thereto.

2. A radio aerial system comprising a number n of traveling wave antennas located along a line perpendicular to a desired direction of transmission and fed in parallel and in equal phase, the said antennas overlapping and each being terminated by a resistance having a value equal to the surge impedance of the antenna connected thereto, each antenna having a width B at least as great as A 1/1? where B is the overall width of the system.

3. A radio aerial system comprising a number n of rhombic antennas located along a line perpendicular to a desired direction of transmission and fed in parallel and in equal phase, the said antennas overlapping along said line and each being terminated by a resistance having a value equal to the surge impedance of each antenna having an antenna connected thereto, the width B at least as great as 2 1/17 where B is the overall width of the system.

4. A radio aerial system comprising a plurality of traveling wave antennas located along a line perpendicular to a desired direction of transmission and fed in parallel and in equal phase, the said antennas overlapping along said line and each being terminated by a resistance having a value equal to the surge impedance of the antenna connected thereto, each of said traveling Wave antennas comprising a plurality of rhombic antennas connected in an end-to-end series relationship along the desired direction of transmission.

5. A radio aerial system comprising a number n of traveling wave antennas located along a line perpendicular to a desired direction of transmission and fed in parallel and in equal phase, the said antennas overlapping along said line, each of said traveling wave antennas comprising a plurality of rhombic antennas connected in an end-to-end series relationship along the desired direction of transmission, each of said series of rhombic antennas being terminated by a resistance having a value equal to the surge impedance of the last rhombic antenna of the series, each rhombic antenna having a width B at least as great as A where B is the overall width of the system.

OTTO BGHM. 

